1. Field of the Invention
The present invention relates to a developing apparatus for use in an electrophotographic recording apparatus, and more particularly relates to a developing apparatus disposed below an image retainer for developing an electrostatic latent image on the image retainer.
2. Description of the Prior Art
In a recording apparatus such as an electrophotographic reproducing machine, an electrostatic latent image is formed on a drum-shaped or belt-shaped image retainer, and the latent image is developed with one-component or two-component developer. In a developing apparatus, a developing roll consisting of a magnet roll having a plurality of magnets and a developing sleeve rotating around the outer peripheral surface of said magnet roll is faced to the image retainer so that a predetermined distance is maintained between the image retainer and the developing sleeve to form a developing region. The latent image on the image retainer is developed with a developer carried on the developing sleeve by applying a developing bias voltage on the developing sleeve.
Normally, in the developing apparatus, the developing roll is disposed on one side of the drum-shaped or belt-shaped image retainer. By such arrangement, it is possible to dispose a transfer means below the image retainer to transfer a toner image developed by the developing apparatus on a recording paper. If such developing apparatus is disposed on one side of the image retainer, however, the developing roll is projected laterally from a body case of the developing apparatus. Accordingly, when the developing apparatus is installed as a unit in the recording apparatus or removed therefrom, developer attached to the developing sleeve may be dropped, so that the recording apparatus may be soiled. However, if the developing roll of the developing apparatus is disposed below the image retainer, the developer does not soil the recording apparatus when the developing apparatus is installed in or removed from the recording apparatus as a unit, because the developing roll faces upwards. It has been proved that the possibility of fog or soil due to the developer in such developing apparatus with the developing roll faced upwards is smaller than that in the other type developing apparatus. The present invention relates to a developing apparatus having a developing roll faced upwards.
In case that a multi-color image is to be obtained, a plurality of developing apparatuses are arranged on a peripheral surface portion of the drum-shaped or belt-shaped image retainer. The total length of the peripheral surface of the drum-shaped or belt-shaped image retainer can be shortened by reducing the length of the peripheral surface occupied by one developing apparatus, in order to increase the recording speed and to minimize the size of the developing apparatus.
In the developing apparatus of reduced width having the developing sleeve faced upwards, a reservoir portion of the developer is provided below the developing roll consisting of the outer developing sleeve and a plurality of inner magnets, and a plurality of rotary agitating screws are disposed in said reservoir portion to circulate and agitate the developer.
A developer layer thickness regulating means for limiting the layer thickness of the developer fed to the developing sleeve is provided on the marginal peripheral surface of the rotary developing sleeve at the upstream side of the developing region. A developer removing means formed of a metallic resilient thin plate or rubber blade etc. is provided on the peripheral surface of the rotary developing sleeve at the downstream side of the developing region to remove from the developing sleeve the developer having been used for the development.
FIG. 3(a) is a plan view of the reservoir portion of the developer in the developing device having the developing roll faced upwards, and FIG. 3(b) is a section along the line A--A of FIG. 3(a).
In said reservoir portion, agitating screws 35a, 35b each having a blade wound herically around the screw are rotated in opposite directions, respectively, by gears 39a, 39b meshed with each other to agitate the developer. In order to agitate and circulate the developer effectively, it is preferable to provide a partition plate 36 of a height as shown by a double dot-and-dash line between the screws 35a, 35b so that the developer is agitated and circulated in directions of arrows shown in FIGS. 3(a) and 3(b). Reference numeral 30 denotes a toner supply port for supplying a toner to the developer which has been used for development.
In said developing apparatus having the developing roll faced upwards, the developer removing means and the partition plate 36 are arranged closely and accordingly it is very difficult to hold them.